Lithium batteries are widely used in consumer electronics due to their relatively high energy density. Rechargeable batteries are also referred to as secondary batteries, and lithium ion secondary batteries generally have a negative electrode material that intercalates lithium or alloys with lithium. For some current commercial batteries, the negative electrode material can be graphite, and the positive electrode material can comprise lithium cobalt oxide (LiCoO2). In practice, only roughly 50% of the theoretical capacity of the cathode can be used, and even a lower percentage is available for longer cycling. At least two other lithium-based cathode materials are also currently in commercial use. These two materials are LiMn2O4, having a spinel structure, and LiFePO4, having an olivine structure. These other materials have not provided any significant improvements in energy density.
Lithium ion batteries can be classified into two categories based on their application. The first category involves high power battery, whereby lithium ion battery cells are designed to deliver high current (Amperes) for such applications as power tools and Hybrid Electric Vehicles (HEVs). However, by design, these battery cells are lower in energy since a design providing for high current generally reduces total energy that can be delivered from the battery. The second design category involves high energy batteries, whereby lithium ion battery cells are designed to deliver low to moderate current (Amperes) for such applications as cellular phones, lap-top computers, Electric Vehicles (EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery of higher total capacity. However, for either category of materials, the batteries should be able to operate at relatively high rates of discharge for period of time.